Digital watermark-embedding apparatus and method, digital watermark-detecting apparatus and method, and recording medium

ABSTRACT

A digital image signal is divided into blocks. Each of the divided blocks is subjected to orthogonal transformation. As a result, the divided blocks are transformed into several frequency components. One or more frequency components are selected in accordance with a characteristic amount that is extracted from the several frequency components. Values of the selected frequency components are operated under a predetermined rule in accordance with an embedment signal that is generated from embedment information.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an apparatus and method forembedding embedment information as digital watermarks into an imagesignal, an apparatus and method for detecting the digital watermarksfrom the image signal, and a medium having a program recorded thereinfor practicing each of the above methods.

[0003] 2. Description of the Related Art

[0004] In recent years, digital content such as digitized audio anddigitized video data has been on the increase. The digital content iseasy to provide a faithful reproduction of original content. Therefore,it is an important issue to protect the copyright of the digitalcontent. Illegally reproduced or distributed content is very difficultto differentiate from corresponding original content. This fact involvesdifficulties in demonstrating an evidence to assert the copyright of thecontent. As a result, efforts have been made to protect the copyright ofthe digital content.

[0005] A “digital watermark” is used as one of the efforts. The digitalwatermark is an art of embedding data into the video data withoutallowing human beings to perceive degradation in image quality, andfurther of detecting the embedded data from the image data having theembedded data embedded therein.

[0006] A prior art digital watermark-embedding apparatus of the typediscussed above has been disclosed in, e.g., published Japanese PatentApplication Laid-Open No. 2000-175161 (patent reference No. 1).

[0007] This prior art is now described with reference to FIG. 18. FIG.18 is a block diagram illustrating the prior art digitalwatermark-embedding apparatus.

[0008] In FIG. 18, a block-dividing unit 1401 divides a moving imageframe (image data) into blocks, while a block-extracting unit 1402extracts one of the blocks, which is designated by a template 1409.

[0009] A DCT unit 1403 practices the DCT processing of the extractedblock. A DCT coefficient-extracting unit 1404 extracts a DCT coefficientdesignated by the template 1409. A watermark data-embedding unit 1405increases an absolute value of a DCT coefficient value, and then embedswatermark data into the DCT coefficient value.

[0010] An inverse DCT unit 1406 performs the inverse DCT of the DCTcoefficient value having the watermark embedded therein, and then feedsa block image into a block-combining unit 1407. The block-combining unit1407 combines the block images together, thereby generating one-frameimage data. The block-combining unit 1407 feeds the one-frame image datainto an MPEG-encoding unit 1408.

[0011] The MPEG-encoding unit 1408 encodes the image data, and thenoutputs compressed image data. For example, an image database serverdelivers the compressed image data to a client.

[0012] However, the prior art requires the above-mentioned processes ofDCT, inverse DCT, and MPEG-encoding in order to distribute thecompressed image data having the digital watermarks embedded therein.

[0013] The embedded watermark data is detected in a manner as discussedbelow.

[0014] An absolute value of a DCT coefficient value of a block havingwatermark data embedded therein is compared with an absolute averagevalue of a corresponding DCT coefficient value of a neighboring block.When the absolute value of the former DCT coefficient value differs fromthe absolute average value of the latter DCT coefficient value by anamount equal or greater than a scheduled threshold value, then it isdetected that the watermark data have been embedded.

[0015] As a result, the embedded watermark data are difficult to detectwhen a block to be detected and its neighboring blocks have greatlydifferent image complexities. For example, a flat image results in a DCTcoefficient having a reduced amount of an alternating current componentvalue. An image abundant with edges causes a DCT coefficient having anincreased amount of alternating current component. According to theprocess as taught by patent reference No. 1, these different imagesintermingled in both of the block to be detected and the neighboringblocks bring about a problem of poor detective precision.

[0016] According to the process of patent reference No. 1, a template isused to determine a block where digital watermarks are embedded. Thisstep may degrade image quality, depending on the complexity of acorresponding image of the determined block. For example, when the blockdetermined by the template is a flat image, then digital watermarkembedment results in deteriorated image quality.

[0017] Such a digital watermark-embedding method is taught in publishedJapanese Patent Application Laid-Open No. 11-75166 (patent reference No.2). Patent reference No. 2 discloses a method for superposing a microlevel of additional information on a several-pixel basis of a videosignal.

[0018] According to patent reference No. 2, a superposing level ofadditional information within on a several-pixel basis is varied topermit a superposing level pattern within on the several-pixel basis tocoincide with a predetermined invariable pattern, thereby superposingthe additional information onto a video signal.

[0019] According to patent reference No. 2, each pixel on a pixel domainis minutely varied to embed digital watermarks, with the result of anincreased amount of processing. For example, in order to embed thedigital watermarks into an originally MPEG-encoded video, extension mustbe at first made to the pixel domain before re-encoding is carried outafter the digital watermark embedment. This means that patent referenceNo. 2 is improper for real-time processing.

OBJECTS AND SUMMARY OF THE INVENTION

[0020] A first object of the present invention is to provide adigital-watermarking art immune to a block image and havinghigh-detective precision.

[0021] A second object of the present invention is to provide adigital-watermarking art for suppressing degradation in image quality.

[0022] A third object of the present invention is to provide adigital-watermarking art that requires a small amount of processing, andthat has a high affinity for standard image-encoding represented byMPEG-encoding.

[0023] A first aspect of the present invention selects one or morefrequency components on the basis of a first characteristic amountextracted from several frequency components, and operates values of theselected one or more frequency components under a predetermined rule inaccordance with a second characteristic amount.

[0024] This feature suppresses degradation in image quality, andrequires a small amount of processing.

[0025] A second aspect of the present invention operates, under apredetermined rule, values of one or more frequency components that haveexperienced discrete cosine transform.

[0026] This feature realizes digital watermark embedment that has a highaffinity for standard image-encoding represented by MPEG-encoding usingthe discrete cosine transform.

[0027] A third aspect of the present invention performs calculationsafter selecting a region having a high level of digital watermarkembedment-caused variations, and a neighboring region adjacent to theformer region and having pixels close in value to those of the formerregion.

[0028] This feature operatively extracts only digital watermarkembedment-caused variations, and realizes a digital-watermarking arthaving high-detective precision and immune to a block image.

[0029] The above, and other objects, features and advantages of thepresent invention will become apparent from the following descriptionread in conjunction with the accompanying drawings, in which likereference numerals designate the same elements.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030]FIG. 1 is a block diagram illustrating a digitalwatermark-embedding apparatus according to a first embodiment of thepresent invention;

[0031]FIG. 2 is a flowchart illustrating how the digitalwatermark-embedding apparatus behaves;

[0032]FIG. 3 is a descriptive illustration showing frequency componentsaccording to the first embodiment;

[0033]FIG. 4 is a descriptive illustration showing an embedment stepaccording to the first embodiment;

[0034] FIGS. 5(a), (d), (g), and (j) illustrate operations according tothe first embodiment;

[0035] FIGS. 5(b), (e), (h), and (k) illustrate amounts of variations inluminance according to the first embodiment;

[0036] FIGS. 5(c), (f), (i), and (l) illustrate distributions of thevariations in luminance according to the first embodiment;

[0037] FIGS. 6(a), (d), (g), and (j) illustrate operations according tothe first embodiment;

[0038] FIGS. 6(b), (e), (h), and (k) illustrate amounts of variations inluminance according to the first embodiment;

[0039] FIGS. 6(c), (f), (i), and (l) illustrate distributions of thevariations in luminance according to the first embodiment;

[0040] FIGS. 7(a), (d), and (g) illustrate operations according to thefirst embodiment;

[0041] FIGS. 7(b), (e), and (h) illustrate amounts of variations inluminance according to the first embodiment;

[0042] FIGS. 7(c), (f), and (i) illustrate distributions of thevariations in luminance according to the first embodiment;

[0043]FIG. 8 illustrates a positional relationship between blocksaccording to the first embodiment;

[0044]FIG. 9 illustrates an MPEG employed according to the firstembodiment;

[0045]FIG. 10 is a block diagram illustrating a digitalwatermark-embedding apparatus according to a second embodiment;

[0046]FIG. 11 is a flowchart illustrating how the digitalwatermark-embedding apparatus behaves;

[0047]FIG. 12 is a descriptive illustration showing regions selectedaccording to the second embodiment;

[0048]FIG. 13 is a descriptive illustration showing neighboring regionsselected according to the second embodiment;

[0049]FIG. 14(a) illustrates a bit string according to a thirdembodiment;

[0050]FIG. 14(b) illustrates pseudo-random number sequences according tothe third embodiment;

[0051]FIG. 15 is a block diagram illustrating a digitalwatermark-embedding apparatus according to a fourth embodiment;

[0052]FIG. 16 is a flowchart illustrating how the digitalwatermark-embedding apparatus behaves;

[0053]FIG. 17 is a descriptive illustration showing a recording mediumhaving programs recorded therein according to the present invention; and

[0054]FIG. 18 is a block diagram illustrating a prior art digitalwatermark-embedding apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0055] Embodiments of the present invention will now be described withreference to the accompanying drawings.

[0056] (First Embodiment)

[0057]FIG. 1 is a block diagram illustrating a digitalwatermark-embedding apparatus according to a first embodiment.

[0058] As seen from FIG. 1, the digital watermark-embedding apparatuscomprises an embedment signal-generating unit 101, a block-diving unit102, an orthogonal transform unit 103, a first characteristicamount-extracting unit 104, a selecting unit 105, and a secondcharacteristic amount-extracting unit 106, and a digitalwatermark-embedding unit 107.

[0059] The embedment signal-generating unit 101 generates, on the basisof embedment information, a signal to be embedded as a digitalwatermark. The block-dividing unit 102 divides a digital image signalinto blocks that are formed by several pixels.

[0060] The orthogonal transform unit 103 practices the orthogonaltransformation of the blocks, thereby transforming the blocks intofrequency components. The digital watermark-embedding unit 107 operatesa value of at least one of the frequency components under apredetermined rule in accordance with the embedment signal from theembedment signal-generating unit 101. In consideration of detection, thevalue of at least one of the frequency components is operated in such amanner that amounts of variations in image within the blocks follow apredetermined pattern.

[0061] The first characteristic amount-extracting unit 104 extracts afirst characteristic amount on the basis of the frequency components.

[0062] The selecting unit 105 selects a value of at least one of thefrequency components on the basis of the extracted first characteristicamount.

[0063] The digital watermark-embedding apparatus according to thepresent invention is further discussed with reference to FIG. 2. FIG. 2is a flowchart illustrating how the digital watermark-embeddingapparatus of FIG. 1 behaves.

[0064] At step 201, the embedment signal-generating unit 101 transformsembedment information into a binary bit string.

[0065] For example, when 16-bit identification information “715” isembedded as embedment information, the embedment signal-generating unit101 transforms embedment information “715” into “0000001011001011” asexpressed by the binary bit string.

[0066] At step 202, the block-dividing unit 102 divides a digital imagesignal into blocks formed by several pixels. Pursuant to the presentembodiment, the divided blocks are eight-by-eight pixels. Such blockshave a high affinity for a MPEG system.

[0067] At step 203, the orthogonal transform unit 103 performsorthogonal transformation of the blocks divided at step 202, therebytransforming the blocks into frequency components. Pursuant to thepresent embodiment, the orthogonal transform unit 103 performs discretecosine transform.

[0068] At step 204, the first characteristic amount-extracting unit 104extracts a first characteristic amount from the frequency componentstransformed at step 203.

[0069] Pursuant to the present embodiment, the first characteristicamount is a total of specific frequency components that correspond tovertical and horizontal edges in an image within the blocks.

[0070] The first characteristic amount is further described withreference to FIG. 3. In FIG. 3, each rectangle is a block that hasexperienced the discrete cosine transform at step 203. Each of therectangles corresponds to one of the frequency components.

[0071] In FIG. 3, assume that a total of specific frequency componentscorresponding to the vertical edges are sumV, and that sumV is a totalof absolute values of frequency components AC1, AC5, and AC6. Furtherassume that a total of specific frequency component corresponding to thehorizontal edges is sumH, and that sumH is a total of absolute values offrequency components AC2, AC3, and AC9.

[0072] In the block image, a value of sumV increases according to thestrength of vertical edge components. As a result, sumV serves as anindex of the strength of the vertical edge components. Meanwhile, sumHserves as an index of the strength of horizontal edge components.

[0073] At step 205, the selecting unit 105 select one or more frequencycomponents on the basis of the first characteristic amount extracted atstep 204.

[0074] Pursuant to the present embodiment, the frequency components areselected according to conditions as discussed below, where “R” is apredetermined threshold.

[0075] condition “a”: frequency component “AC1” in FIG. 3 is selectedwith sumV>R and sumH≦R;

[0076] conditions “b”: frequency component “AC2” in FIG. 3 is selectedwith sumH>R and sumV≦R;

[0077] conditions “c”: frequency components “AC1” and “AC2” in FIG. 3are selected when neither condition “a” nor condition “b” is applicable.

[0078] At step 206, the second characteristic amount-extracting unit 106extracts a second characteristic amount from the digital image signalthat is designated by the frequency components transformed at step 203.

[0079] Pursuant to the present embodiment, the second characteristicamount is a direct current component value plus a total of specificalternating current component values. In FIG. 3, the direct currentcomponent value is a value of frequency component “DC”, while the totalof specific alternating current component values is a total of values offrequency components “AC1” to “AC9”.

[0080] The direct current component value “DC” designates a luminanceaverage value of pixels in the blocks. The total of specific alternatingcurrent component values “AC1” to “AC9” increases in value according tothe complexity of the block image, and thus serves as an index ofcomplexity.

[0081] At step 207, the digital watermark-embedding unit 107 allocates avalue of the bit string (generated at step 201) to each of the blocks,and then fluctuates values of one or more frequency components (selectedat step 205) on the basis of the second characteristic amount extractedat step 206, thereby embedding digital watermarks into the frequencycomponents.

[0082]FIG. 4 shows how the bit string is allocated to each of theblocks. According to the present embodiment, as shown in FIG. 4, a valueof the bit string is repeatedly allocated to every other block.

[0083] Assume that a frequency component to be fluctuated has originalvalue “Xorg” and fluctuation value “dX”. Assume that a fluctuatedfrequency component has value “Xwm”.

[0084] Assume that the fluctuated frequency component has value “Xwm”equal to “Xorg”+“dx” (“Xwm”=“Xorg”+“dX”) when value “1” of the bitstring is allocated.

[0085] Assume that the fluctuated frequency component has value “Xwm”equal to “Xorg”−“dx” (“Xwm”=“Xorg”−“dX”) when value “0” of the bitstring is allocated.

[0086] Fluctuation value “dX” is a positive value, and fluctuates withrespect to a reference value in accordance with the direct currentcomponent value and the specific alternating current component values.Direct current component “DC” responds with the luminance average value.Accordingly, fluctuation value “dX” is desirably increased when thedirect current component “DC” assumes a value at which visualcharacteristics of human beings are difficult to perceive variations,but fluctuation value “dX” is preferably reduced when the direct currentcomponent “DC” assumes a value at which the visual characteristics ofthe human beings are easy to perceive the variations.

[0087] An increased total of specific alternating current componentvalues “AC1” to “AC9” brings about a complicated image that is abundantwith edge components. As a result, it is difficult to perceive thevariations. Conversely, a reduced total of specific alternating currentcomponent values “AC1” to “AC9” results in a flat image, and it is easyto perceive the variations.

[0088] Accordingly, fluctuation value “dX” is desirably increased withan increase in total of the specific alternating current componentvalues, but is desirably decreased with a decrease in total thereof. Thedigital watermark-embedding unit 107 provides such control over valuesof the frequency components selected at step 205.

[0089] Referring to the frequency components having digital watermarksembedded therein as described above, a pixel value on a pixel domain isminutely varied for each of the blocks. An amount of such a variation isrepresented by either a single pattern of a basic image in discretecosine transform or a combination of several patterns.

[0090] FIGS. 5 to 7 illustrate variations in luminance values in theblocks having the digital watermarks embedded therein.

[0091] FIGS. 5(a), (d), (g), (j), FIGS. 6(a), (d), (g), (l), FIGS. 7(a),(d), and (g) illustrate operations by which the digital watermarks areembedded.

[0092] FIGS. 5(b), (e), (h), (k), FIGS. 6(b), (e), (h), (k), FIGS. 7(b),(e), and (h) illustrate distribution (specific patterns) of amounts ofvariations in luminance.

[0093] FIGS. 5(c), (f), (i), (l), FIGS. 6(c), (f), (i), (l), FIGS. 7(c),(f), and (i) schematically illustrate the above distribution usingpositive and negative sings.

[0094] FIGS. 5(a), (b), and (c) illustrates step 205 where condition “b”is fulfilled. Similarly, FIGS. 5(d), (e), and (f) illustrates step 205where condition “a” is met. FIGS. 5(g), (h), and (i) illustrates step205 where condition “c” is met.

[0095] In addition to conditions “a”, “b”, and “c”, conditions as shownin FIGS. 5(j) to 5(l), FIG. 6, and FIG. 7 may be established to embedthe digital watermarks into the frequency components.

[0096] At any rate, as illustrated in FIGS. 5(c), (f), (i), (l), FIGS.6(c), (f), (i), (l), FIGS. 7(c), (f), and (i), the specific patterns areregularly formed in such a manner that each region having a positiveamount of image variations and each region having a negative amount ofimage variations are arranged in alternating sequence. Such specificpatterns provide regular amounts of variations in luminance in responseto the embedment of the digital watermarks. Such regularity facilitatesdetecting the digital watermarks, and further avoids missing the digitalwatermarks.

[0097] The digital watermark-embedding apparatus according to thepresent embodiment selects one or more frequency components on the basisof the first characteristic amount that has been extracted from severalfrequency components, and then operates values of the selected one ormore frequency components under a predetermined rule on the basis of thesecond characteristic amount. This feature suppresses degradation inimage quality.

[0098] The digital watermark-embedding apparatus according to thepresent embodiment requires a small amount of processing, and furtheroperates values of one or more discrete cosine-transformed frequencycomponents under a predetermined rule. This feature realizes digitalwatermark embedment having a high affinity for standard image-encodingrepresented by MPEG-encoding using discrete cosine transform.

[0099] Pursuant to the present embodiment, embedment information istransformed into a binary bit string at step 201. However, the presentinvention is not limited thereto.

[0100] Pursuant to the present embodiment, the digital image signal isdivided at step 202 into the blocks formed by eight-by-eight pixels.However, the present invention is not limited thereto. Alternativeblocks formed by four-by-four pixels may be employed.

[0101] Pursuant to the present embodiment, the discrete cosine transformis used as orthogonal transformation at step 203. However, the presentinvention is not limited thereto. Alternatively, any other transform maybe used as long as it is orthogonal transformation. For example, wavelettransform is acceptable.

[0102] Pursuant to the present embodiment, a total of specific frequencycomponents corresponding to vertical and horizontal edges are used asthe first characteristic amount at step 204. However, the presentinvention is not limited thereto. Alternatively, examples as illustratedin FIGS. 5 to 7 or others may be used.

[0103] As a further alternative, specific frequency componentscorresponding to slanted edges may be used. An extracted characteristicamount suited for visual characteristics of human beings operativelymakes it difficult to perceive degradation in image quality.

[0104] Pursuant to the present embodiment, a characteristic amount of anembedment block is extracted at step 204. Alternatively, in addition tothe characteristic amount of the embedment block, characteristic amountsof blocks (hereinafter called neighboring blocks) adjacent to theembedment block may also be extracted. In this case, at step 205, one ormore frequency components may be selected on the basis of thecharacteristic amount of the embedment block and the characteristicamounts of the neighboring blocks. This alternative step is effective infurther inhibiting the degradation in image quality.

[0105] For example, there is available an alternative method in which adetermination may be made at step 205 to see how conditions “a” to “c”are applicable to the embedment block and the neighboring blocks, withthe result that the condition to be applicable to the embedment block isdecided by majority.

[0106]FIG. 8 illustrates the embedment block and the neighboring blocks.In FIG. 8, symbols “a”, “b”, and “c” in the blocks denote conditions“a”, “b”, and “c”, respectively. This means that the block designed by,e.g., “a” is applicable to condition “a”.

[0107] As seen from FIG. 8, the embedment block is applicable tocondition “c”. At the same time, the blocks applicable to condition “b”including the neighboring blocks are the greatest in number. In thiscase, the embedment block may alternatively be applicable to condition“b” as majority decision.

[0108] Pursuant to the present embodiment, frequency component “AC1” or“AC2”, or both of them are selected at step 205 on the basis of thefirst characteristic amount. However, the present invention is notlimited thereto. It is desirable to select a frequency component suchthat the selected frequency component is closer to an image patternillustrated by the first characteristic amount, when the selectedfrequency component is operated under a predetermined rule.

[0109] Pursuant to the present embodiment, direct current componentvalue “DC” and a total of specific alternating current components “AC1”to “AC9” are used as the second characteristic amount at step 206.However, the present invention is not limited thereto. Alternatively, acharacteristic amount adapted for visual characteristics of human beingsmay be extracted. Such an extracted characteristic amount effectivelymakes it difficult to perceive degradation in image quality.

[0110] Pursuant to the present embodiment, each value of a bit string isrepeatedly allocated to every other block at step 207. However, thepresent invention is not limited thereto as long as a value of the bitstring is allocated regularly to each block. In this case, all that isrequired is that the digital watermark-embedding apparatus and a digitalwatermark-detecting apparatus share such an allocation method.

[0111] Pursuant to the present embodiment, a fluctuated frequencycomponent has value “Xwm” equal to “Xorg”+“dX” when an allocated valueof the bit string is “1”, but the fluctuated frequency component hasvalue “Xwm” equal to “Xorg”−“dX” when an allocated value of the bitstring is “0”. However, the use of “dX” having contrary signs providessimilar effects. Pursuant to the present embodiment, the value of thefrequency component is operated under a predetermined rule to fluctuatethe frequency component value. However, such a fluctuation is only anexample of the operation under the predetermined rule.

[0112] Pursuant to the present embodiment, a digital image signal isdivided into blocks, each of which is then subjected to orthogonaltransformation. Thereafter, one or more frequency component values areoperated in a predetermined manner, thereby embedding digital watermarksinto the frequency components. Alternatively, an MPEG stream, e.g., maybe decoded to a level at which one or more frequency component valuesdenote the MPEG stream, thereby embedding the digital watermarks intothe frequency components. This alternative step provides similarbeneficial effects.

[0113]FIG. 9 illustrates an example in which the digitalwatermark-embedding apparatus of FIG. 1 is employed in a MPEG system ofcompressed image data.

[0114] As illustrated in FIG. 9, compressed image data of the MPEGsystem enters a separating unit 901, and the separating unit 901separates the compressed image data. The separated image data is fedinto a variable length-decoding unit 902 from the separating unit 901.The variable length-decoding unit 902 practices the variable lengthdecoding of the separated compressed image, and then feeds DCTcoefficient values (frequency components) into the digitalwatermark-embedding unit 107.

[0115] As previously described, the digital watermark-embedding unit 107embeds digital watermarks into the DCT coefficient values. The DCTcoefficient values having the digital watermarks embedded therein aresent to a variable length-encoding unit 903 from the digitalwatermark-embedding unit 107. The variable length-encoding unit 903practices the variable length encoding of the DCT coefficient valueshaving the digital watermarks embedded therein. The variablelength-encoded DCT values are sent to a multiplexing unit 904.

[0116] As discussed above, the embedment of the digital watermarks intothe DCT coefficients (frequency components) eliminates a series ofprocesses such as inverse DCT encoding, block combining, and encodingfrom a pixel domain, when compared with the prior art as illustrated inFIG. 18.

[0117] As a result, a step of embedding the digital watermarks into MPEGsystem of compressed image data retained in, e.g., a video server, todeliver the embedded image data to a client provides advantages of asmall number of processes, lighter processing loads on the video serve,and a good response to the client.

[0118] An image of a pixel domain is obtained when an inversequantization unit 905 inverse-quantizes the output of the variablelength-decoding unit 902, and subsequently the inverse DCT unit 906practices the inverse DCT of the inverse-quantized output. Asillustrated by dashed lines in FIG. 9, the digital watermark embedmentis allowable immediately after the inverse quantization.

[0119] (Second Embodiment)

[0120] A second embodiment is now discussed with reference to thedrawings. The present embodiment discuses a digital watermark-detectingapparatus operable to detect digital watermarks from an image signalhaving the digital watermarks embedded therein by the digitalwatermark-embedding apparatus as described in the previous embodiment.

[0121]FIG. 10 is a block diagram illustrating a structure of the digitalwatermark-detecting apparatus according to the present embodiment.

[0122] In FIG. 10, the digital watermark-detecting apparatus comprisesan input unit 701, a block-dividing unit 702, a region-selecting unit703, a calculating unit 704, a bit-detecting unit 705, a bitstring-determining unit 706, and a detected bit string output unit 707,and an adjacent region-selecting unit 708

[0123] The image signal enters the input unit 701. The block-dividingunit 701 divides the image signal from the input unit 701 into blocksthat are formed by several pixels. The region-selecting unit 703 selectsregions within the blocks. The calculating unit 704 performspredetermined calculation based on the selected regions.

[0124] The bit-detecting unit 705 detects a value of an embedded bit onthe basis of an output value from the calculating unit 704. The bitstring-determining unit 706 determines an embedded bit string on thebasis of the bit value detected by the bit-detecting unit 705.

[0125] The detected bit string output unit 707 outputs the bit stringdetermined by the bit string-determining unit 706. The adjacentregion-selecting unit 708 selects neighboring regions adjacent to theregions selected by the region-selecting unit 703.

[0126] The digital watermark-detecting apparatus according to thepresent invention is further discussed with reference to FIG. 11. FIG.11 is a flowchart illustrating how the digital watermark-detectingapparatus of FIG. 10 behaves.

[0127] At step 801, an image signal having digital watermarks embeddedtherein enters the input unit 701.

[0128] At step 802, the block-dividing unit 702 divides the enteredimage signal into blocks that are formed by several pixels. Pursuant tothe present embodiment, the divided blocks are formed by eight-by-eightpixels.

[0129] At step 803, the region-selecting unit 703 selects severalregions from within the blocks divided at step 802. Each of the regionsconsists of one or more pixels.

[0130]FIG. 12 shows how the regions are selected from the blocks ofeight-by-eight pixels according to the present steps. In FIG. 12, eachrectangle corresponds to a single pixel.

[0131] As illustrated in FIG. 12, regions “A” and “B” are selected. Inselecting the regions, it is desirable to select pixels that exhibit ahigh level of digital watermark embedment-caused variations.

[0132] The above selection is made in such a manner as to correspond tofrequency components fluctuated by the digital watermark-embeddingapparatus according to the previous embodiment. As a result, theselected regions are varied according to the frequency componentsfluctuated in the digital watermark embedment. In this regard, refer toFIGS. 5 to 7.

[0133] Referring back to FIG. 11, at step 804, the adjacentregion-selecting unit 708 selects several regions adjacent to theregions selected at step 803. Each of such adjacent regions consists ofone or more pixels.

[0134]FIG. 13 illustrates how the neighboring regions are selectedaccording to the present steps. In FIG. 13, regions “C” and “D”contiguous to the regions “A” and “B”, respectively, are selected.

[0135] In selecting the regions “C” and “D”, it is desirable to selectregions containing pixels that are closest in value to the pixels of theregions “A” and “B” selected at step 803, and that exhibit littlevariations in response to the digital watermark embedment. According tothe present embodiment, the region “C” has the pixels closest in valueto those of region “A”, while the region “D” has the pixels closest invalue to those of the regions “B”.

[0136] No variations result from the digital watermark embedment becausea bit string to be embedded is allocated to every other block using thedigital watermark-embedding apparatus according to the previousembodiment.

[0137] At step 805, the calculating unit 704 performs predeterminedcalculation of the regions selected at steps 803 and 804. Assume thatthe selected regions “A”, “B”, “C”, and “D” have the pixels summing upto sumA, sumB, sumC, and sumD, respectively. In this instance, an outputvalue is equal to (sumA−sumC)−(sumB−sumD).

[0138] Alternatively, “sumA−sumB” may be taken as an output value todetect digital watermarks. However, this alternative is likely to detectthe digital watermarks with poor precision, depending upon how thepixels within the blocks are varied in value. In view of the above, sumCand sumD of the regions “C” and “D” having the pixels close in value tothose of the regions “A” and “B” respectively are subtracted from sumAand sumB, respectively. As a result, only variations caused by thedigital watermark embedment are operatively extractable.

[0139] At step 806, the embedded bit is detected according to the outputvalue in step 805 to determine that the embedded bit has values of “0”or “1”. When the output value in step 805 is positive, then the bitvalue is “1”. When the output value in step 805 is negative, then thebit value is “0”.

[0140] At step 807, the bit string-determining unit 706 determines theembedded bit string on the basis of the bit values detected at step 806.The bit string-determining unit 706 arranges in sequence the valuesdetected for each of the blocks at step 806, thereby forming a bitstring.

[0141] The digital watermark-embedding apparatus according to theprevious embodiment embeds the bit string repeatedly. Accordingly, thebit string circulating within an image frame is detectable. The valuesin the bit string are determined by majority decision in accordance withthe repeatedly detected bit string.

[0142] At step 808, the detected bit string output unit 707 outputs thebit string determined at step 807.

[0143] As described above, the digital watermark-embedding apparatusaccording to the present embodiment performs calculations afterselecting a region having a high level of digital watermarkembedment-caused variations and an adjacent region having pixels closein value to pixels of the former region, in which no digital watermarkembodiment-caused variations occur in the adjacent region. As a result,only digital watermark embedment-caused variations are effectivelyextractable. A digital watermarking art immune to a block image anddesigned to detect digital watermarks with high precision is achievable.

[0144] Pursuant to the present embodiment, a total of pixel valueswithin each of the regions are determined at step 805 to calculatedifferences in pixel value between the regions. Alternatively, anaverage of pixel values within each of the regions is acceptable. As afurther alternative to the simple total of pixel values, the pixelvalues may be weighted according to amounts of variations in pixels inresponse to the digital watermark embedment.

[0145] Pursuant to the present embodiment, at steps 803 and 804, theregions are selected from the present frame image where blocks to bedetected are present. In addition thereto, the regions may be selectedin sequence of regeneration from the previous frame, the subsequentframe, or both of them. This alternative provides further pronounceddetection of digital watermarks. In this instance, it is desirable toselect, from the previous frame or subsequent frame, blocks nearest inimage to the blocks to be detected.

[0146] (Third Embodiment)

[0147] A third embodiment is now described with the drawings. A digitalwatermark-embedding apparatus according to the present embodimentdiffers in only step 201 (see FIG. 2) from that according to the firstembodiment. The embedment signal-generating unit 101 (see FIG. 1) takesstep 21. Therefore, the present embodiment discusses only an embedmentsignal-generating unit 101.

[0148] The embedment signal-generating unit 101 selects a pseudo-randomnumber sequence that corresponds to embedment information, withreference to a reference table in which the previously preparedembedment information is related to pseudo-random number sequences. Theembedment signal-generating unit 101 generates an embedment signal fromthe selected pseudo-random number sequence. Each bit of the generatedembedment signal is allocated to one of the blocks.

[0149] The present embodiment employs a reference table having thepseudo-random number sequences related to a position and values of eachbit that forms a binary bit string transformed from the embedmentinformation. The embedment information is transformed into the binarybit string in a manner identical to the first embodiment.

[0150] A subsequent process is now discussed with reference to FIG. 14.FIG. 14(a) illustrates the binary bit string transformed from theembedment information and bit positions of the binary bit string. FIG.14(b) illustrates the reference table in which each of the pseudo-randomnumber sequences is related to a corresponding bit position and values.

[0151] The embedment signal-generating unit 101 selects thepseudo-random number sequences according to the reference tablesequentially from the head of the bit string. For example, as seen fromFIG. 14(a), bit position {0} corresponds to a bit having value {0}.Accordingly, as illustrated in FIG. 14(b), pseudo-random number {S000}is selected. As a result, each bit of pseudo-random number {S000} isallocated to one of the blocks.

[0152] As described above, the bit string of the embedment informationis related to the pseudo-random number sequences to perform digitalwatermark embedment.

[0153] The present embodiment uses the reference table having thepseudo-random number sequences related to the bit position and values ofeach bit that forms the binary bit string transformed from the embedmentinformation. An alternative reference table may be used, in which eachof the pseudo-random number sequences is related to a corresponding bitposition and values for every several bits of the embedment information.As a further alternative, as long as any reference table designed touniquely determine corresponding embedment information from each of thepseudo-random number sequences is available, the present invention isnot limited to the reference table as already discussed. All that isrequired is that the digital watermark-embedding apparatus and thedigital watermark-detecting apparatus may share the reference table.

[0154] (Fourth Embodiment)

[0155] A fourth embodiment is now discussed with reference to thedrawings. The present embodiment discusses a digital watermark-detectingapparatus operable to detect digital watermarks from an image signalhaving the digital watermarks embedded therein by the digitalwatermark-embedding apparatus according to the third embodiment.

[0156]FIG. 15 is a block diagram illustrating the digitalwatermark-detecting apparatus according to the present embodiment.

[0157] In FIG. 15, the digital watermark-detecting apparatus comprisesan input unit 701, a block-dividing unit 702, a region-selecting unit703, a calculating unit 704, a sequence-recording unit 1201, acorrelation value-calculating unit 1202, a threshold-setting unit 1203,a comparing unit 1204, a bit string-determining unit 706, a detected bitstring output unit 707, and an adjacent region-selecting unit 708.

[0158] The sequence-recording unit 1201 retains a reference table inwhich each piece of embedment information is related to a pseudo-randomnumber sequence.

[0159] The correlation value-calculating unit 1202 calculates valuescorrelated between a sequence of output values calculated by thecalculating unit 704 for each block and the pseudo-random numbersequences included in the reference table, and then feeds the maximum ofthe obtained correlation values into the comparing unit 1204.

[0160] The threshold-setting unit 1203 sets up a threshold of thecorrelation value. The comparing unit 1204 compares the maximumcorrelation value from the correlation value-calculating unit 1202 withthe threshold from the threshold-setting unit 1203, thereby providing apseudo-random number sequence met by results from the comparison. Thepseudo-random number sequence is sent to the bit string-determining unit706.

[0161] The bit string-determining unit 706 determines a bit string to beembedded, on the basis of the pseudo-random number sequence from thecomparing unit 1204 and the reference table. The detected bit stringoutput unit 707 outputs the bit string determined by the bitstring-determining unit 706.

[0162] The digital watermark-detecting apparatus according to thepresent embodiment is further discussed with reference to FIG. 16.

[0163]FIG. 16 is a flowchart illustrating how the digitalwatermark-detecting apparatus of FIG. 15 behaves.

[0164] At step 1301, an image signal having digital watermarks embeddedtherein enters the input unit 701.

[0165] At step 1302, the block-dividing unit 702 divides the imagesignal into blocks that are formed by several pixels. Pursuant to thepresent embodiment, the divided blocks are formed by eight-by-eightpixels.

[0166] At step 1303, the region-selecting unit 703 selects severalregions from within the divided blocks. The several regions consist ofone or more pixels. Since step 1303 is identical to step 803 (see FIG.11) according to the second embodiment, descriptions related thereto areomitted.

[0167] At step 1304, the adjacent region-selecting unit 708 selectsseveral regions adjacent to the regions selected at step 1303. Theadjacent regions consist of one or more pixels. Since step 1304 isidentical to step 804 (see FIG. 11) according to the second embodiment,descriptions related thereto are omitted.

[0168] At step 1305, the calculating unit 704 performs predeterminedcalculation of the regions selected at steps 1303 and 1304. Since step1305 is identical to step 805 (see FIG. 11) according to the secondembodiment, descriptions related thereto are omitted.

[0169] The sequence-recording unit 1201 records the same content as thereference table having the pseudo-random number sequence related toembedment information according to the third embodiment.

[0170] At 1306, the correlation value-calculating unit 1202 calculatesvalues correlated between a sequence of output values calculated foreach of the blocks at step 1305 and all of the pseudo-random numbersequences in the reference table recorded by the sequence-recording unit1201, and then determines the maximum from among the calculatedcorrelation values. The correlation value-calculating unit 1202 feeds,into the comparing unit 1204, the maximum correlation value and one ofthe pseudo-random number sequences, which provides such a correlation.

[0171] Referring to the reference table of FIG. 14(b), the correlationvalue-calculating unit 1202 determines values correlated betweenthirty-two pseudo-random number sequences {S000, S001 through S151} anda sequence of output values calculated for each of the blocks, and thendetermines the maximum from among the determined correlation values.When maximum correlation value SMAX is obtained from a correlation withpseudo-random number sequence {S000}, maximum correlation value SMAX andpseudo-random number sequence {S000} are sent to the comparing unit1204.

[0172] At step 1307, the threshold-setting unit 1203 sets up a thresholdfor the comparing unit 1204. At step 1308, the comparing unit 1204compares the maximum correlation value with the threshold. When thecorrelation value is greater than the threshold, then a bit positioncorresponding to the pseudo-random number sequence that provides themaximum correlation value, and values of the bit position are sent tothe bit string-determining unit 706. Referring to the reference table ofFIG. 14(b), bit position {0} corresponding to pseudo-random numbersequence {S000}, and value {0} of bit position {0} are sent to the bitstring-determining unit 706. No processing is made when the maximumcorrelation value is less than the threshold.

[0173] When illegal reproduction causes disturbances, there are caseswhere correlation values greater than the threshold may be all absent,or where several correlation values greater than the threshold mayexist. In this instance, the comparing unit 1204 takes an exceptionalstep, not comparing the threshold with the correlation value. Morespecifically, only when maximum correlation value “S1” is related toother correlation values “Sn” under a certain condition (e.g., S1>Sn),then the comparing unit 1204 may determine a bit position correspondingto a pseudo-random number sequence that provides maximum correlationvalue “S1”, and values of the bit position.

[0174] At step1309, the bit string-determining unit 706 retains the bitposition and values thereof from the comparing unit 1204, and then formsa bit string when all bit positions of an embedded bit string and valuesof the bit positions are fully provided. The formed bit string is sentto the detected bit string output unit 707.

[0175] At step 1310, the detected bit string output unit 707 outputs thebit string determined at step 1309.

[0176] As described above, the digital watermark-detecting apparatusaccording to the present embodiment detects embedded digital watermarkson the basis of a correlation with a pseudo-random number sequencerelated to an embedment signal, and consequently provideshigher-reliable detection when compared with a method of simplydetecting a bit string.

[0177] The first to fourth embodiments have been discussed as above.

[0178] Typically, as shown in FIG. 17, the digital watermark-embeddingapparatus and digital watermark-detecting apparatus according to thefirst to fourth embodiments provide features achieved by a storage unit1502 (ROM, RAM, hard disk, etc.) and a CPU 1501 (central processingunit). The storage unit 1502 is operable to contain a digitalwatermark-embedding program and a digital watermark-detecting program.The CPU 1501 is operable to execute such program data. The digitalwatermark-embedding program and digital watermark-detecting program arecontained in a recording media 1505 such as a CD-ROM and a floppy disk,and are then loaded or installed into the storage unit 1502 from therecording medium 1505.

[0179] The present invention selects one or more frequency components onthe basis of a first characteristic amount extracted from severalfrequency components, and then operates values of the selected one ormore frequency components under a predetermined rule. This featuresuppresses degradation in image quality. The present invention extractsa second characteristic amount from several frequency components thathas experienced orthogonal transform, and then embeds digital watermarksinto the frequency components in accordance with the secondcharacteristic amount. This feature further suppresses the degradationin image quality.

[0180] The present invention requires a small amount of processing. Thepresent invention operates, under a predetermined rule, values of one ormore frequency components that have experienced discrete cosinetransform. This feature realizes digital watermark embedment having ahigh affinity for standard image encoding represented by MPEG-encodingusing the discrete cosine transform.

[0181] The present invention performs calculations after selecting aregion having a high level of digital watermark embedment-causedvariations, and a neighboring region adjacent to the former region andclose in pixel value to the former region, in which no digital watermarkembedment-caused variations occur in the neighboring region. Thisfeature operatively extracts only variations caused by digital watermarkembedment, and realizes a digital-watermarking art having high-detectiveprecision.

[0182] Having described preferred embodiments of the invention withreference to the accompanying drawings, it is to be understood that theinvention is not limited to those precise embodiments, and that variouschanges and modifications may be effected therein by one skilled in theart without departing from the scope or spirit of the invention asdefined in the appended claims.

What is claimed is:
 1. A digital watermark-embedding apparatuscomprising: an embedment signal-generating unit operable to generate anembedment signal in accordance with embedment information, the embedmentsignal being embedded as a digital watermark; a block-dividing unitoperable to divide a digital image signal into blocks that are formed byseveral pixels; an orthogonal transform unit operable to practiceorthogonal transformation of each of the blocks, thereby transformingthe blocks into several frequency components; and a digitalwatermark-embedding unit operable to operate, under a predeterminedrule, a value of at least one of the several frequency components inaccordance with the embedment signal generated by said embedmentsignal-generating unit, in which the value is operated in such a mannerthat amounts of variations in image within the blocks follow apredetermined specific pattern in consideration of detection.
 2. Adigital watermark-embedding apparatus as defined in claim 1, wherein thespecific pattern has two different regions arranged in alternatingsequence, one of the two different regions being where the amounts ofvariations in image serve as positive, and the other region being wherethe amounts of variations in image serve as negative.
 3. A digitalwatermark-embedding apparatus as defined in claim 1, wherein theembedment signal-generating unit transforms the embedment informationinto a binary bit string, thereby using the binary bit string as theembedment signal.
 4. A digital watermark-embedding apparatus as definedin claim 1, wherein said embedment signal-generating unit selects apseudo-random number sequence corresponding to the embedmentinformation, with reference to a reference table having pseudo-randomnumber sequences related to previously prepared embedment information,and uses the selected pseudo-random number sequence as the embedmentsignal.
 5. A digital watermark-embedding apparatus as defined in claim1, further comprising: a first characteristic amount-extracting unitoperable to extract a first characteristic amount in accordance with theseveral frequency components; and a selecting unit operable to select avalue of at least one of the several frequency components in accordancewith the extracted first characteristic amount.
 6. A digitalwatermark-embedding apparatus as defined in claim 5, wherein said firstcharacteristic amount-extracting unit extracts the first characteristicamount in accordance with several frequency components in the blocks andseveral frequency components in neighboring blocks positioned adjacentto the former blocks.
 7. A digital watermark-embedding apparatus asdefined in claim 5, wherein the first characteristic amount is acombination of one or greater sorts selected from a total of specificfrequency components corresponding to vertical edges in an image withinthe blocks, a total of specific frequency components corresponding tohorizontal edges therein, and a total of specific frequency componentscorresponding to slanted edges therein.
 8. A digital watermark-embeddingapparatus as defined in claim 7, wherein said selecting unit determines,in accordance with the first characteristic amount, which one of thevertical edges, the horizontal edges, and the slanted edges is dominantin the image within the blocks, and selects at least one of the severalfrequency components in accordance with results from the determination.9. A digital watermark-embedding apparatus as defined in claim 1,wherein said digital watermark-embedding unit operates the value inorder to fluctuate the value.
 10. A digital watermark-embeddingapparatus as defined in claim 1, wherein said orthogonal transform unitperforms a discrete cosine transform.
 11. A digital watermark-embeddingapparatus as defined in claim 10, wherein the specific pattern includesa pattern represented by a base image in the discrete cosine transform.12. A digital watermark-embedding apparatus as defined in claim 9,further comprising: a second characteristic-extracting unit operable toextract a second characteristic amount from the several frequencycomponents, wherein said digital watermark-embedding unit changes, inaccordance with the extracted second characteristic amount, magnitude atwhich the value is fluctuated.
 13. A digital watermark-embeddingapparatus as defined in claim 12, wherein the several frequencycomponents include a direct current component value and a specificalternating current component value, and wherein the secondcharacteristic amount is either one of the direct current componentvalue and the specific alternating current component value or both. 14.A digital watermark-detecting apparatus comprising: an input unitoperable to receive an image signal; a block-dividing unit operable todivide the received image signal into blocks that are formed by severalpixels; a region-selecting unit operable to select a region within theblocks; a calculating unit operable to practice predeterminedcalculation based on the selected region; a bit-detecting unit operableto detect a value of an embedded bit in accordance with an output valuefrom said calculating unit; a bit string-determining unit operable todetermine an embedded bit string in accordance with the bit valuedetected by said bit-detecting unit; and a detected bit string outputunit operable to output the bit string determined by said bitstring-determining unit.
 15. A digital watermark-detecting apparatuscomprising: an input unit operable to receive an image signal; ablock-dividing unit operable to divide the received image signal intoblocks that are formed by several pixels; a region-selecting unitoperable to select a region within the blocks; a calculating unitoperable to practice predetermined calculation based on the selectedregion; a sequence-recording unit operable to retain a reference tablehaving pseudo-random number sequences related to embedment information;a correlation value-calculating unit operable to calculate values ofcorrelation between a sequence of output values calculated by saidcalculating unit for each of the blocks and the pseudo-random numbersequences included in the reference table, thereby outputting a maximumcorrelation value of the obtained correlation values; athreshold-setting unit operable to set a threshold of the correlationvalue; a comparing unit operable to compare the maximum correlationvalue from said correlation value-calculating unit with the thresholdset by said threshold-setting unit, thereby outputting one of thepseudo-random number sequences, which is met by results from thecomparison; a bit string-determining unit operable to determine anembedment bit string in accordance with the pseudo-random numbersequence from said comparing unit and the reference table; and adetected bit string output unit operable to output the bit stringdetermined by said bit string-determining unit.
 16. A digitalwatermark-detecting apparatus as defined in claim 14, furthercomprising: a neighboring region-selecting unit operable to select aneighboring region positioned adjacent to the region selected by saidregion-selecting unit, wherein said calculating unit performspredetermined calculation based on the region selected byregion-selecting unit and the neighboring region selected by saidneighboring region-selecting unit.
 17. A digital watermark-detectingapparatus as defined in claim 14, wherein said region-selecting unitselects the region within the blocks from at least one of, in sequenceof reproduction, a previous frame before a present frame in which theblocks exist and a subsequent frame after the present frame, in additionto the present frame.
 18. A digital watermark-detecting apparatus asdefined in claim 16, wherein said neighboring region-selecting unitselects the neighboring region positioned adjacent to the regionselected by said region-selecting unit, from at least one of, insequence of reproduction, a previous frame before a present frame inwhich the blocks exist and a subsequent frame after the present frame,in addition to the present frame.
 19. A digital watermark-embeddingmethod comprising: generating an embedment signal in accordance withembedment information, the embedment signal being embedded as a digitalwatermark; dividing a digital image signal into blocks that are formedby several pixels; practicing orthogonal transformation of each of theblocks, thereby transforming the blocks into several frequencycomponents; and operating, under a predetermined rule, a value of atleast one of the several frequency components in accordance with theembedment signal obtained by the generating the embedment signal, inwhich the value is operated in such a manner that amounts of variationsin image within the blocks follow a predetermined specific pattern inconsideration of detection.
 20. A digital watermark-embedding method asdefined in claim 19, wherein the specific pattern has two differentregions arranged in alternating sequence, one of the two differentregions being where the amounts of variations in image serve aspositive, and the other region being where the amounts of variations inimage serve as negative.
 21. A digital watermark-embedding method asdefined in claim 19, wherein said generating the embedment signalcomprises transforming the embedment information into a binary bitstring, thereby using the transformed binary bit string as the embedmentsignal.
 22. A digital watermark-embedding method as defined in claim 19,wherein said generating the embedment signal comprises selecting apseudo-random number sequence corresponding to the embedmentinformation, with reference to a reference table having pseudo-randomnumber sequences related to previously prepared embedment information,and using the selected pseudo-random number sequence as the embedmentsignal.
 23. A digital watermark-embedding method as defined in claim 19,further comprising: extracting a first characteristic amount inaccordance with the several frequency components; and selecting at leastone of the several frequency components in accordance with the extractedfirst characteristic amount.
 24. A digital watermark-embedding method asdefined in claim 23, wherein said extracting the first characteristicamount comprises extracting the first characteristic amount inaccordance with several frequency components in the blocks and severalfrequency components in neighboring blocks positioned adjacent to theformer blocks.
 25. A digital watermark-embedding method as defined inclaim 23, wherein the first characteristic amount is a combination ofone or greater sorts selected from a total of specific frequencycomponents corresponding to vertical edges in an image within theblocks, a total of specific frequency components corresponding tohorizontal edges therein, and a total of specific frequency componentscorresponding to slanted edges therein.
 26. A digitalwatermark-embedding method as defined in claim 25, wherein saidselecting at least one of the several frequency components comprisesdetermining, in accordance with the extracted first characteristicamount, which one of the vertical edges, the horizontal edges, and theslanted edges is dominant in the image within the blocks, and selectingat least one of the several frequency components in accordance withresults from the determination.
 27. A digital watermark-embedding methodas defined in claim 19, wherein said operating the value under thepredetermined rule is to fluctuate the value.
 28. A digitalwatermark-embedding method as defined in claim 20, wherein saidpracticing the orthogonal transformation comprises performing a discretecosine transform.
 29. A digital watermark-embedding method as defined inclaim 28, wherein the specific pattern includes a pattern represented bya base image in the discrete cosine transform.
 30. A digitalwatermark-embedding method as defined in claim 28, further comprising:extracting a second characteristic amount from the several frequencycomponents, wherein said operating the value under the predeterminedrule comprises changing, in accordance with the extracted secondcharacteristic amount, magnitude at which the value is fluctuated.
 31. Adigital watermark-embedding method as defined in claim 30, wherein theseveral frequency components include a direct current component valueand a specific alternating current component value, and wherein thesecond characteristic amount is either one of the direct currentcomponent value and the specific alternating current component value orboth.
 32. A digital watermark-detecting method comprising: receiving animage signal; dividing the received image signal into blocks that areformed by several pixels; selecting a region within the blocks;practicing predetermined calculation based on the selected region;detecting a value of an embedded bit in accordance with an output valueobtained by said practicing the predetermined calculation; determiningan embedded bit string in accordance with the detected bit value that isobtained by said detecting the value of the embedded bit; and outputtingthe determined bit string that is obtained by said determining theembedded bit string.
 33. A digital watermark-detecting methodcomprising: receiving an image signal; dividing the received imagesignal into blocks that are formed by several pixels; selecting a regionwithin the blocks; practicing predetermined calculation based on theselected region; retaining a reference table having pseudo-random numbersequences related to embedment information; calculating values ofcorrelation between a sequence of output values calculated by saidpracticing the predetermined calculation for each of the blocks and thepseudo-random number sequences included in the reference table, therebyoutputting a maximum correlation value of the obtained correlationvalues; setting a threshold of the correlation value; comparing themaximum correlation value with the threshold, thereby outputting one ofthe pseudo-random number sequences, which is met by results from thecomparison; determining an embedment bit string in accordance with thepseudo-random number sequence that is outputted by said comparing themaximum correlation value with the threshold, and the reference table;and outputting the determined bit string that is obtained by saiddetermining the embedment bit string.
 34. A digital watermark-detectingmethod as defined in claim 32, further comprising: selecting aneighboring region positioned adjacent to the region selected by saidselecting the region, wherein said performing predetermined calculationcomprises performing predetermined calculation based on the regionselected by said selecting the region and the neighboring regionselected by said selecting the neighboring region.
 35. A digitalwatermark-detecting method as defined in claim 32, wherein saidselecting the region comprises selecting the region within the blocksfrom at least one of, in sequence of reproduction, a previous framebefore a present frame in which the blocks exist and a subsequent frameafter the present frame, in addition to the present frame.
 36. A digitalwatermark-detecting method as defined in claim 32, wherein saidselecting the neighboring region comprises selecting the neighboringregion positioned adjacent to the region selected by said selecting theregion, from at least one of, in sequence of reproduction, a previousframe before a present frame in which the blocks exist and a subsequentframe after the present frame, in addition to the present frame.
 37. Arecording medium having a digital watermark-embedding program recordedtherein to be readable by a computer, the digital watermark-embeddingprogram comprising: generating an embedment signal in accordance withembedment information, the embedment signal being embedded as a digitalwatermark; dividing a digital image signal into blocks that are formedby several pixels; practicing orthogonal transformation of each of theblocks, thereby transforming the blocks into several frequencycomponents; and operating, under a predetermined rule, a value of atleast one of the several frequency components in accordance with theembedment signal obtained by said generating the embedment signal, inwhich the value is operated in such a manner that amounts of variationsin image within the blocks follow a predetermined specific pattern inconsideration of detection.
 38. A recording medium having a digitalwatermark-detecting program recorded therein to be readable by acomputer, said digital watermark-detecting program comprising: receivingan image signal; dividing the received image signal into blocks that areformed by several pixels; selecting a region within the blocks;practicing predetermined calculation based on the selected region;detecting a value of an embedded bit in accordance with an output valueobtained by said practicing the predetermined calculation; determiningan embedded bit string in accordance with the detected bit value that isobtained by said detecting the value of the embedded bit; and outputtingthe determined bit string that is obtained by said determining theembedded bit string.
 39. A digital watermark-embedding apparatuscomprising: a separating unit operable to separate a compressed imagesignal; a variable length-decoding unit operable to practice variablelength-decoding of the separated compressed image signal, therebyoutputting frequency components; a digital watermark-embedding unitoperable to embed digital watermarks into the outputted frequencycomponents; a variable length-encoding unit operable to practicevariable length-encoding of the frequency components having the digitalwatermarks embedded therein; and a multiplexing unit operable tomultiplex the compressed image signal that has experienced the variablelength-encoding.